How Liquid Motion Lamps Work


Image courtesy Melanie Tsoi/Stock.xchng

Since their first appearance in the 1960s, liquid motion lamps have been a familiar fixture in college dorms and teenagers' bedrooms all over the world. In the United States and many other countries, the novelty devices have become completely entrenched in popular culture. Even after all these years, people are still buying motion lamps, and the major manufacturers now offer hundreds of variations on the basic design!

In this article, we'll look at these popular devices to find out exactly what happens inside to produce such a mesmerizing display. We'll also explore some of the history behind liquid motion lamps, and even get you started on making your own basic lamp. The next time you see a motion lamp, you'll definitely be transfixed, because you'll know all about the amazing processes at work.

Inside the Lamp

Liquid motion lamps are actually fairly simple devices. They are based on very basic scientific principles and consist of only a few simple components. They must have:

  • A compound that makes up the floating "blobs"
  • A compound that the blobs float in
  • A lamp that illuminates the display and provides the heat necessary to move the blobs

To create the floating blobs, the two compounds in a motion lamp must be immiscible, or mutually insoluble. All this means is that liquid A doesn't dissolve in liquid B -- the two don't mix, so you see two separate liquids, one floating on top of or within the other.

­­The classic example of immiscible compounds is oil and water. If you fill a jar with common mineral oil and water, you'll get a water layer with a layer of oil floating above it. This combination of water and oil in a jar has a similar look to a commercial motion lamp with its light turned off; in a cold lamp you see two separate layers.

The coolest thing about motion lamps, of course, is that they produce distinct amorphous blobs that rise and fall in the lamp's "globe" on their own. To produce this effect, you need to pick your two insoluble compounds very carefully. In our oil and water jar, the water ends up on the bottom because it has a much higher density than oil. Simply put, a liquid with a higher density pushes a lower-density liquid upward (for more on this, check out How Helium Balloons Work).

To get blobs that will float around, you need two substances that are very similar in density, so that the blobs can easily switch between rising and sinking. Then you need to be able to change the density of one of the compounds so that sometimes it is lighter than the other compound (and so floats to the top) and sometimes it is heavier (so that it sinks to the bottom). We'll look at how to do this in the next section.

­

Heating a Motion Lamp

The most common way to change the density of compounds is to change their temperature. Heating a compound activates the molecules so that they spread apart, making the compound less dense. If you have read How Thermometers Work, you know that heating water causes it to expand quite a bit. Cooling the compound down again increases the density.

If you look inside a motion lamp when it's turned off, you'll find a solid waxy compound on the bottom of the globe. This solid compound is only a little denser than the surrounding liquid compound. When you turn on the light at the base of the globe, here is what happens:

  • The solid quickly turns into a liquid and expands, giving it a lower density than the surrounding liquid.
  • A warm blob is now slightly less dense than the surrounding liquid, so it rises to the top of the globe.
  • Because it is farther away from the heat source, the blob cools slightly, becoming more dense than the surrounding liquid (it does not cool down enough to change back into a solid, however).
  • The blob sinks to the bottom of the globe, where it heats up enough to rise again.

This is a pretty simple idea, but it's actually fairly complicated to balance all the elements -- the compounds, the heat source and the size of the globe -- so that the blobs are constantly moving around. In fact, the companies that produce commercial motion lamps guard their ingredients very closely, and motion lamp enthusiasts have had a very hard time reproducing the displays you see in commercial models.

In the next section, we'll look at the history of the liquid motion lamp.

Motion Lamp History

Image courtesy Donald Cook/Stock.xchng

The invention of this type of motion lamp is generally credited to a man named Edward Craven Walker, although there is a certain amount of controversy surrounding its actual origins. One widespread account is that Walker came up with the basic design in the 1950s while developing a complicated egg timer in England. Another version of the story is that Walker got the idea from a simpler liquid motion lamp he saw in a pub. In any case, Walker was definitely the man who molded this idea into its current form and started it on its way to becoming a popular cultural icon. Walker died in August 2000, at the age of 82.

Walker worked on his motion lamp, which he called the Astro Light, for almost a decade before finally launching it in 1963. His U.K.-based company, Cresworth, achieved some success with the device, but the lamp design really took off when the U.S. company Lava Manufacturing Corp. formed in 1965. The company was founded by two Chicago entrepreneurs, Adolph Wertheimer and Hy Spector, who discovered Walker's Astro Light at a trade show in Germany. They acquired the U.S. patent rights and began producing a line of their own motion lamps. These lamps soon caught on as a must-have decoration for the counterculture crowd.

This company, now called Lava World International, still produces almost all of the commercial models sold in U.S. stores. Their product is called a Lava Lite®, not a Lava Lamp, but both terms are trademarked. Like Xerox and Kleenex, "Lava Lamp" is commonly used as a generic term, but intellectual property law does not recognize it as such. Lava World International closely monitors how publishers print the word "lava" in connection with motion lamps.

When the Lava Lite caught on in the United States, Walker's Astro Light grew in popularity in Europe. Sales dropped off in the 1980s, however, and Walker sold the Astro Light rights to Cressida Granger. Her company, Mathmos, continues to produce lamps for the market outside the United States. The company has expanded its line considerably over the years, offering many innovative, modern variations on the basic lamp design.

Both Mathmos and Lava World International have enjoyed a "motion lamp renaissance" that began in the early 1990s as part of a 1960s nostalgia trend. Astro Light and Lava Lite sales are still going strong today, and there are lots of motion lamp fans out there, at least judging by the number of motion lamp sites populating the Web.

Next, we'll show you how to build your own liquid motion lamp.

Make Your Own Motion Lamp

There are a number of Web sites that offer instructions on how to create your own liquid motion lamp.

You won't find any plans with the exact same material found in a commercial lamp, because this information is still top secret. Motion lamp recipes are so popular because coming up with exactly the right compound combination is an exciting chemistry puzzle. It's a real trick finding two compounds that will form the free-floating blobs you see in commercial lamps.

One of the simpler plans out there uses mineral oil as the blobs and a combination of 70-percent and 90-percent rubbing alcohol as the surrounding liquid. The trick with these ingredients is to balance the two different grades of rubbing alcohol until you get a good balance between the alcohol's density and the density of the oil.

You can color the blobs by adding insoluble dye, such as the sort used in permanent markers. For best results, you should find a fairly tall glass container for the globe. For a safe and effective lamp, don't use anything hotter than a 40-watt bulb to heat the globe. To learn how to make this basic motion lamp, check out this page.

Other homemade motion lamp designs use more complicated combinations of materials to create better displays. In most cases, acquiring all the necessary ingredients for building a lamp yourself is actually more expensive than simply buying a commercial model. It is an interesting project, however, and it's an excellent way to fully explore how liquid motion lamps work.

If you are interested in making your own lamp, keep in mind that dealing with these sorts of materials and constructing any device with a heating unit is potentially hazardous. Don't undertake such a project unless you have a good knowledge of the materials involved or you are assisted by someone who does. Make sure you aren't handling any dangerous chemicals and, as with any chemistry experiment, wear eye protection and an apron. Most of the sites that feature motion lamp plans also include disclaimers disavowing any responsibility because they are fully aware of the potential dangers involved.

To learn more about the history and construction of motion lamps, check out the links on the next page. You'll also find plenty of pictures of the many commercial motion lamp designs released through the years.

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